Method of etching zirconium diboride

ABSTRACT

A thin film of zirconium diboride that has been deposited onto a substratend patterned using photolithography is dry etched in a commercial plasma etcher with either chloride gas, or a mixture of a chloride gas with oxygen, or a mixture of a chloride gas with nitrogen, or a mixture of chloride gas with a noble gas, or a fluoride gas, or a mixture of a fluoride gas with oxygen, or a mixture of a fluoride gas with nitrogen, or a mixture of a fluoride gas with a noble gas.

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto us of any royalty thereon.

This invention relates in general to a method of etching zirconiumdiboride, ZrB₂ and in particular to a method of dry etching a thin filmof ZrB₂ that has been deposited onto a substrate and patterned usingphotolithography.

BACKGROUND OF THE INVENTION

U.S. patent application Ser. No. 156,124, filed 16 Feb., 1988, of LindaS. Heath for "Method of Etching Titanium Diboride" and assigned to acommon assignee and with which this application is copending describesand claims a method of etching titanium diboride with a dry etch.

Zirconium diboride, like titanium diboride, TiB₂, has become of interestin laboratory research because of its resistance to change ordegradation at high temperatures. However, zirconium diboride doesexhibit other properties that differ significantly from the propertiesof titanium diboride. That is, ZrB₂ is twice as electrically conductiveas TiB₂. Moreover, the melting point of ZrB₂ is 3245° C. as compared to2980° C., the melting point of TiB₂. The higher melting point makesZrBhd more resistant to changes with heat. Then too, ZrB₂ is less porousthan TiB₂.

One of the difficulties involved with working with ZrB₂ is that becauseof its resistance to attack, it is difficult to pattern. In fact, no wetetches have been available to carry out such patterning.

SUMMARY OF THE INVENTION

The general object of this invention is to provide a method of etchingZrB₂. A more particular object of this invention is to provide a methodof etching a thin film of ZrB₂ that has been deposited onto a substrateand patterned using photolithography.

It has now been found that the aforementioned objects can be attained byetching ZrB₂ with a dry etch.

More particularly, according to the invention, a thin film of ZrB₂ thathas been deposited onto a substrate and patterned using photolithographyis dry etched by first mounting the substrate bearing the patterned thinfilm on the lower electrode of a pair of electrodes in the etch chamberof a commercial plasma etcher or plasma therm etcher. The etch chamberis evacuated to a pressure of about 10⁻⁶ Torr and a dry etchant as forexample, tetrafluoromethane (CF₄) or dichlorodifluoromethane (CCl₂ F₂)admitted at a flow rate of about 1 to 100 sccm and a pressure set atabout 1 to 500 mTorr. An electric field is applied between theelectrodes, the power level set at about 50 to 1000 watts and etchingallowed to proceed for the desired time.

Other dry etchants that will etch ZrB₂ include a chloride gas or amixture of chloride gas with oxygen or a mixture of a chloride gas withnitrogen or a mixture of chloride gas with a noble gas or a fluoride gasor a mixture of a fluoride gas with nitrogen or a mixture of a fluoridegas with a noble gas.

After the dry etch, the sample is removed and the etch rate determinedby measuring the etch depth and dividing by the etch time.

By adjusting the process parameters, one is able to attain etch rates of67 to 140 Å/min for ZrB₂. This is useful for patterning ZrB₂ as adiffusion barrier or a Schottky contact to semiconductors.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A thin film of ZrB₂ is first deposited on a gallium arsenide substrateby sputtering and the substrate with thin film of ZrB₂ then patternedusing photolithography.

The substrate bearing the patterned film is then mounted on the lowerelectrode of a pair of electrodes in the etch chamber of a commercialplasma etcher. The etch chamber with the electrodes inside is thenevacuated to a pressure of about 10⁻⁶ Torr. CCl₂ F₂ is then admittedinto the etch chamber at a flow rate of about 2 to 10 sccm and thepressure set at about 10 to 50 mTorr. An electric field is appliedbetween te electrodes and the power level set at about 300 watts. Theetch is allowed to proceed until the ZrB₂ is completely removed in theareas exposed by the photolithography.

Other dry etch processes that can be used to etch ZrB₂ include reactiveion beam etching (RIBE), chemically assisted ion beam etching (CAIBE),reactive ion etching (RIE), and magnetron ion etching (MIE).

We wish it to be understood that we do not desire to be limited to theexact details as described for obvious modifications will occur to aperson skilled in the art.

What is claimed is:
 1. Method of etching a thin film of zirconiumdiboride that has been deposited onto a substrate and patterned usingphotolithography, said method including the steps of:(A) mounting asubstrate bearing a patterned thin film on a lower electrode of a pairof electrodes in an etch chamber of a plasma therm etcher, (B)evacuating teh etch chamber to a pressure of about 10⁻⁶ Torr, (C)admitting a dry etchant to the etch chamber at a flow rate of about 1 to100 sccm and a pressure set at about 1 to 500 mTorr, (D) applying anelectric field between the pair of electrodes and setting the powerlevel at about 50 to 1000 watts, and (E) allowing the etch to proceedfor a predetermined time.
 2. Method according to claim 1 wherein the dryetchant is selected from the group consisting of a chloride gas, amixture of a chloride gas with oxygen, a mixture of a chloride gas withnitrogen, a mixture of a chloride gas with a noble gas, a fluoride gas,a mixture of a fluoride gas with oxygen, a mixture of a fluoride gaswith nitrogen, and a mixture of a fluoride gas with a noble gas. 3.Method according to claim 2 wherein the dry etchant is a chloride gas.4. Method according to claim 3 wherein the dry etchant isdichlorodifluoromethane.
 5. Method according to claim 2 wherein the dryetchant is a mixture of a chloride gas with oxygen.
 6. Method accordingto claim 2 wherein the dry etchant is a mixture of a chloride gas withnitrogen.
 7. Method according to claim 2 wherein the dry etchant is amixture of a chloride gas with a noble gas.
 8. Method according to claim2 wherein the dry etchant is a fluoride gas.
 9. Method according toclaim 2 wherein the dry etchant is a mixture of a fluoride gas withoxygen.
 10. Method according to claim 2 therein the dry etchant is amixture of a fluoride gas with nitrogen.
 11. Method according to claim 2wherein the dry etchant is a mixture of a fluoride gas with noble gas.